1. Technical Field
The present invention relates to a semiconductor device and a termination region structure thereof, and particularly to a semiconductor device having a trench structure and a termination region structure thereof.
2. Related Art
A Schottky diode is a semiconductor device formed by a metal-semiconductor junction, and due to its low turn-on voltage and high respond speed, it is widely used in various electronic circuits such as power conversion circuits at present. The conventional Schottky diode structure includes a heavily doped semiconductor substrate, which is usually made of monocrystalline silicon; and a semiconductor layer served as a cathode region, which is made of a material doped with a low concentration of the carrier having conductivity identical to that of the substrate. Moreover, a metal layer or a metal silicide layer is formed on the cathode region lightly doped, so as to form a Schottky barrier and constitute an anode of the diode.
The Schottky diode has a characteristic of fast speed, and only requires a low forward bias; in other words, the Schottky diode may have a large forward current and short reverse recovery time. However, when a reverse bias continues to increase, there will be a large leakage current (depending on the work function of the metal and the doping concentration of the semiconductor). Therefore, a trench Schottky diode in the prior art pinches off a reverse leakage current by filling polysilicon or metal in the trenches.
For the conventional trench Schottky diode, reference can be made to U.S. published patent application No. US 2010/0327288. FIG. 1(a) illustrates a trench Schottky diode device according to the application, which includes: a semiconductor substrate 12 having a multi-trench structure 11; a first mask layer 13, formed on a surface of the semiconductor substrate 12; a gate oxide layer 14, formed on a surface of the multi-trench structure 11, where the gate oxide layer 14 protrudes from the surface of the semiconductor substrate 12; a polysilicon structure 15, formed on the gate oxide layer 14, where the polysilicon structure 15 protrudes from the surface of the semiconductor substrate 12; a second mask layer 16, formed on the first mask layer 13 and part of the polysilicon structure 15; and a metal sputtering layer 17, formed on part of surfaces of the second mask layer 16, the semiconductor substrate 12, the polysilicon structure 15 and the gate oxide layer 14.
In addition, a manufacturing process of the trench Schottky diode in FIG. 1(a) includes the following steps: providing a semiconductor substrate (12); forming a first mask layer (13) on the semiconductor substrate (12); etching the semiconductor substrate (12) according to the first mask layer (13), so as to form a multi-trench structure (11) in the semiconductor substrate (12); forming a gate oxide layer (14) on a surface of the multi-trench structure (11); forming a polysilicon structure (15) on the gate oxide layer (14) and the first mask layer (13); etching the polysilicon structure (15), so as to expose a top surface and part of side surfaces of the first mask layer (13); forming a second mask layer (16) on part of the polysilicon structure (15) and part of the first mask layer (13), so as to expose part of surfaces of the semiconductor substrate (12), the polysilicon structure (15) and the gate oxide layer (14); forming a metal sputtering layer (17) on the second mask layer (16) and part of the surfaces of the semiconductor substrate (12), the polysilicon structure (15) and the gate oxide layer (14); and etching the metal sputtering layer (17), so as to expose part of a surface of the second mask layer (16).
However, in the termination region of the conventional trench Schottky diode, polysilicon in a plurality of trenches is not electrically connected to the metal layer, so that the plurality of trenches is in a floating potential state when the device is operated in a reverse bias. The electric field distribution of the termination region cannot be extended and dispersed, resulting in strong electric field crowding, and the breakdown voltage cannot be effectively improved. Accordingly, there are still restrictions on applications thereof for semiconductor devices with higher power or voltage, and how to design and manufacture a Schottky diode with a high breakdown voltage and a low reverse leakage current becomes an urgent issue needs to be solved.